[TigersEye]

One thing I am suspicious of is that the heat could be going right out the windows since all the floor vents are situated next to windows.

I know that seems counter-intuitive but that is normal. The idea is that windows chill the air and cold air falls so the heat vents are located below them to put rising warm air there cutting the amount of cold transferred from the window to the air.

[AlmaKing]

Quite interesting.

[HiTech RedNeck]

But normally the vents don’t blow right up against the window. That would increase heat loss.